Radiation beams have been used to treat (for example necrotize) diseased tissue (e.g. a tumor). However, the radiation beam can also damage healthy tissue. Thus, methods have been used to determine a location of a VOI so that the radiation beam can be focused on a VOI or other diseased tissue. For example, the radiation beam can move over time to minimize exposure of healthy tissue while staying focused on the VOI. An x-ray can be taken at the beginning of the treatment for positioning markers (for example sensors, fiducials or other marking objects) that have been surgically placed on the VOI, thereby providing the location of the VOI. This invasive method is costly and can be dangerous to the patient.
Some methods restrict a patient to a specified position for the duration of a treatment so that the position of the VOI stays known. Such restriction can be quite uncomfortable for the patient, and errors can occur due to imperfect restriction. Methods can take repeated x-rays of internal markers to update the position of the VOI while breathing, but such methods expose the patient to a large amount of radiation via the numerous x-rays or require the motion to be periodic. Methods can omit the implantation of markers (for example fiducials) by correlating a location of certain bones, which tend not to move during treatment, to the VOI location. But, the patient is still restricted to a particular position, or at least a particular orientation (e.g. lying flat on one's back). These methods also still suffer from numerous x-rays if the location of the VOI is to be updated.
U.S. patent publication 2008/0212737 omits the numerous x-rays during treatment and the implantation of markers (for example fiducials) while still accounting for the movement due to breathing; however, the patient is still restricted to certain positions. For example, the patient is restricted to lying on his/her back on a special table while being held in place. A scan is performed at different times during the breathing cycle, with each time in the breathing cycle corresponding to a distance in positions of a marker on the patient's chest compared to a marker in the special table. The scans can then be used to determine a location of the VOI during radiation beam treatment, but the location is accurate only when the person is in the same exact location as when the scans were taken. Thus, although procedure is non-invasive and limits excessive radiation scans during treatment, the person is still confined and uncomfortable during treatment. Furthermore, this application only handles small periodic motion such as breathing. Different positions of the patient are not allowed.
Additionally, the equipment for creating the radiation beam must be precisely calibrated so that a control input corresponds to the exact location where the VOI is determined to be. The equipment must be made with very high tolerance so that the control inputs correspond the proper beam placement. Thus, the beam equipment can be very expensive. Additionally, current techniques do not properly handle beam positioning error.
Therefore it is desirable to have improved systems and methods for providing targeted radiation treatment that can variously allow a patient freedom of movement without excessive radiation, are easy to use, do not require difficult calibration, are non-invasive, allow movement beyond simply breathing, and compensate for beam positing error and other systematic errors in the system.